As a method for producing a disulfonyl fluoride compound, the following methods have been proposed.
(1) A method of subjecting FSO2(CH2)3SO2F to electrolytic fluorination reaction to obtain FSO2CF2CF2CF2SO2F (Non-Patent Document 1).
(2) A method of subjecting cyclic tetrafluoroethylene polysulfide to oxidative ring opening with chlorine and hydrogen peroxide to obtain ClSO2(CF2)2SO2Cl, and fluorinating it with potassium fluoride to obtain FSO2(CF2)2SO2F (Non-Patent Document 2).
(3) A method of converting I(CF2)pI (wherein p is 3, 4 or 6) to ClSO2(CF2)pSO2Cl with sodium sulfinate and chlorine and fluorinating it with potassium fluoride to obtain FSO2(CF2)pSO2F (Non-Patent Document 3).
(4) A method of subjecting ethylene and a compound represented by the following formula (A) to electrolytic coupling reaction to obtain a compound represented by the following formula (C) (wherein q is 1 or 2) (Non-Patent Document 4):FSO2(CF2)2OCFCF(CF3)COOH  (A)FSO2(CF2)2OCFCF(CF3)(CH2CH2)qCF(CF3)O(CF2)2SO2F  (C)
Further, a method of reacting FSO2CF2CF2CF2SO2F obtained by electrolytic fluorination with ammonia to obtain a cyclic perfluoroaliphatic disulfonimide ammonium salt (Patent Document 1) has been known.    Patent Document 1: JP-A-57-146766, Example 3    Non-Patent Document 1: “Journal of Fluorine Chemistry”, 1987, vol. 35, pages 329 to 341    Non-Patent Document 2: “Journal of Fluorine Chemistry”, 1998, vol. 89, pages 107 to 109    Non-Patent Document 3: “Journal of Fluorine Chemistry”, 1993, vol. 63, pages 85 to 100    Non-Patent Document 4: “Journal of Electroanalytical Chemistry”, 1992, vol. 325, pages 167 to 184